Rotary-displacement compressors



March 4, 1969 s N R EI'AL 3,430,848

ROTARY-DISPLACEMENT COMPRESSORS Sheet Filed Dec. 30, 1966 March 4, 1969 s. B. TURNER ETAL ROTARY-DISPLACEMENT v COMPRESSORS Filed D60. 30, 1966 Sheet o fiz 5 6 7 8 9 10 TIME (MINS) ZOO wwwa United States Patent 8,032/66 us. or. 230-210 In. or. F04c 29/04; F04!) 39/06 6 Claims ABSTRACT OF THE DISCLOSURE Overheating of a Roots blower when running near zero delivery against pressure is reduced by means of a cooling-air injection pipe arranged at the inlet side and direction of cooling air into the zone of intermesh, from which the injected air can escape through the inlet pipe.

This invention relates to rotary-displacement machines, a term which is intended to signify compressors and motors in which chambers of periodically increasing and decreasing volume, formed at the circumference of one or more rotary bodies are, in the case of a compressor, used to produce a pressure difference between an inlet and an outlet connection provided at points corresponding to different volumes of these chambers, or are, in the case of a motor, employed to produce a torque upon the rotary bodies, and the invention offers particular advantages in displacement machines of the gear type or of the so-called Roots type, which employs a pair of cooperating rotors having intermeshing projections and recesses.

When a gear-type or Roots-type compressor is operated against riding pressure, a point will eventually be reached at which the volumetric efficiency falls to zero because leakage losses due to return flow through working clearances, so-called recirculation losses, become equal to the fluid intake of the rotors. The power supplied under these circumstances is dispersed as heat in the compressor, and since no fluid is drawn from the intake line, the temperature of the rotors and easing of the compressor is liable to rise excessively. Similar conditions may also arise in certain applications of rotary-displacement motors, for example in a motor used as the auxiliary motor of the constant-speed drive described and claimed in our U.S.A. application No. 38,671, filed June 24, 1960, now Patent No. 3,298,250, where this motor is at times employed to oppose rotation, and where for this purpose its delivery side may, under certain operating conditions, be substantially sealed. In that case rotation of the motor does not involve any appreciable passage of fluid through the motor, thus involving the risk of serious overheating, a risk which in operation under other conditions is absent due to the cooling effect of the air or other fluid passing through the motor. Cooling of the external casing would increase the temperature difference between the rotor, which would become very hot, and the cooled casing, so that, in order to avoid seizure, the normal working clearances in the motor or compressor would have to be increased, thus reducing the volumetric and adiabatic efliciency of the unit and aggravating the recirculation heating effect.

According to the present invention the risk of overheating is reduced by providing the displacement machine with means which are adapted to apply, under such conditions, a jet of cool air (or other working fluid) to the rotor or rotors at the low-pressure side so long as the throughput of the machine is nil or very 3,430,848 Patented Mar. 4, 1969 low. This cooling fluid will strike the surface of the rotor or rotors, so as to become heated by cooling these, and will then escape through the low-pressure connection, taking heat with it by convection. Since the cooling fluid, after striking the rotors, will also be in contact with the housing, the rotor and housing will becooled to approximately equal degrees, thus avoiding the creation of excessive temperature differences between the rotors and the housing.

In the accompanying drawing:

FIGURE 1 is an axial section of one form of a Roots type displacement machine equipped with one form of cooling device according to the present invention.

FIGURE 2 is a temperature-over-time diagram containing two curves, respectively indicating the temperature of the machine housing without the use of cooling means, and when cooling is effected in accordance with the present invention.

Referring now first to FIGURE 1, a Roots-type displacement machine comprises a housing 1 in which two identical rotors 2 and 3, synchronised in a wellknown manner by phasing gears schematically indicated at 4 and 5, rotate in intermeshing relation. The housing 1 has two opposite ports 6 and 7 so that, for the direction of rotation of the rotors indicated by the arrow X, the port 6 may be called the inlet port and port 7 delivery or outlet port. To each of these ports a pipeline 8 or 9 is attached. An air-injection pipe 10 projects inot the inlet port 6 through the pipe line 8. It terminates in the axial direction of the line 8 and is connected at its other end through on-off control means 12 to a source 11 of cooling air under pressure. A jet of cooling air can therefore be blown through pipe 10 towards the zone of intermesh of the two rotors 3 and 4.

The illustrated device was tried in a Roots blower having a swept volume of cubic inches per revolution. This blower was driven at a speed of 5,250 revolutions per minute and operated at pressure ratio of 2:1, the clearances provided being such that under these conditions no effective delivery took place. Curve A in FIGURE 2 indicates the temperatures of the casing 1 reached under these conditions as a function of time, and it will be noticed that the temperature after 8 minutes had reached 210 C. and was still rising rapidly. Curve B similarly shows the temperatures reached by operation, under the same conditions otherwise, when cooling air was injected at a rate of 5 lbs. per minute through the pipe 10. In this case the temperature reached after 8 minutes was only approximately C., and the temperature-time curve shows already a considerable levelling off, so that the temperature can be expected not to rise above approximately C. even after prolonged operation under these conditions.

What we claim is:

1. A rotary-displacement machine, comprising a housing having an operating cavity which includes, spaced from each other along the periphery of said cavity, a high-pressure chamber portion having a high-pressure port, and a low-pressure chamber portion having a lowpressure port, rotor means mounted in the housing for rotation in the cavity and constructed to separate said high pressure chamber portion from said low-pressure chamber portion and to form inside said cavity a plurality of mutually separate displacement chambers which each, during the rotation of the rotor means, increase in volume when passing from the high-pressure chamber portion to the low-pressure chamber portion and decrease in volume when passing from the low-pressure chamber portion to the high-pressure chamber portion, and fluid-injection means operable in the absence of flow of working fluid from one to the other of said two ports to direct, inside said low-pressure chamber portion, a jet of cooling fluid on to the rotor means while permitting an equivalent amount of working fluid to return from said low-pressure chamber portion to said low-pressure port.

2. A rotary-displacement machine as claimed in claim 1 wherein the intermeshing rotors are lobed and form a high-pressure zone at one side and a low-pressure zone at the other side of a zone of intermesh.

3. A method of operating the rotary-displacement machine claimed in claim 1, characterised in that the injection means are fed with fluid which is substantially identical with the working fluid of the machine.

4. A rotary-displacement machine as claimed in claim 1, which includes on/ofl control means for said fluidinjection means.

5. A method of operating the rotary-displacement machine claimed in claim 4, characterised in that said control means is operated to render said injection means operative when the throughput of working fluid between said ports is small compared to the volumetric displacement of the rotor means at their rate of rotation.

6. A method of operating the rotary-displacement ma chine claimed in claim 4, characterised in that the injection means are fed with fluid which apart from its temperature is substantially identical with the working fluid of the machine, and that said on-off control means is operated to render said injection means operative when the throughput of working fluid between said ports is small compared to the volumetric displacement of the rotor means at their rate of rotation.

References Cited UNITED STATES PATENTS 2,489,887 11/1949 Houghton 230-210 2,721,694 10/1955 Van Atta 23014l 3,059,396 10/1963 Thees 230l41 XR FOREIGN PATENTS 772,350 4/ 1957 Great Britain. 838,074 6/1960 Great Britain.

DONLEY J. STOCKING, Primary Examiner.

LEONARD H. GERIN, Assistant Examiner.

US. Cl. X.R. 

